Fluororubbers have excellent chemical resistance, solvent resistance, and heat resistance, and are widely used in various fields such as automobile industries, semiconductor industries, and chemical industries. In the automobile industries, for example, fluororubbers are used as hoses, sealing materials and the like used for engines and peripheral devices thereof, automatic transmissions, fuel systems and peripheral devices thereof, and the like.
In some cases, however, fluororubbers such as propylene-tetrafluoroethylene copolymer rubbers embrittle at low temperatures. Patent Document 1 suggests a method which solves such a problem by blending an ethylene-tetrafluoroethylene copolymer resin [ETFE] having a melting point of 240° C. to 300° C., melt-kneading the mixture, and irradiation cross-linking or peroxide cross-linking the mixture.
Patent Document 2 also teaches a method of producing a cross-linked rubber having better hot strength by pressure cross-linking a fluororubber composition including a fluororubber (a vinylidene fluoride [VdF] rubber), a fluororesin [ETFE], and a fluorine-containing thermoplastic elastomer (at 160° C. for 10 minutes), and further cross-linking the composition in an oven (at 180° C. for 4 hours).
These Patent Documents do not mention the surface properties, particularly the friction characteristics, of the cross-linked rubber. This is because rubbers naturally have a high coefficient of friction because of the elastomeric properties.
In the fields of sealing materials or other products, suggested methods of reducing the coefficient of friction while taking advantage of the characteristics of rubber include a method of laminating, for example, a fluororesin (or a fluororesin fibrous layer) on the surface of the rubber (Patent Documents 3 and 4), and a method of forming a coating film of a fluororesin on the surface of the rubber (Patent Document 5).    Patent Document 1: JP 50-32244 A    Patent Document 2: JP 6-25500 A    Patent Document 3: JP 7-227935 A    Patent Document 4: JP 2000-313089 A    Patent Document 5: JP 2006-292160 A